Manufacturing processes often require that the straightness of the profile of an object be accurately determined. For example, bearing surfaces such as crankshaft journals are required to be straight within a given tolerance. Failure to conform to the specified tolerance requires that a particular crankshaft be rejected or reworked, owing to the fact that the out-of-straight condition is likely to result in premature bearing failure.
Various devices and methods for measuring straightness have been proposed and used in the past. The simplest of these involves the use of a dial indicator in conjunction with a straightedge and fixturing device. The practice of this method is subject to errors and inaccuracies based primarily on the skill of the operator involved. The set up and test procedure must be carefully controlled or the results from the test are substantially without meaning.
More sophisticated straightness tests can be performed with precision electronic equipment, for example, laser interferometers or noncontacting capacitive probes. Owing to the high cost of such equipment, the tests are best performed in an inspection laboratory, and are not practical for production floor use. In addition, highly skilled technicians must be utilized to operate such sophisticated inspection devices.
For the reasons set forth above, none of the devices currently available for measuring the straightness of crankshaft journals and other cylindrical surfaces requiring accurate straightness are suited for a production environment. Therefore, 100% production testing is impractical, and only spot inspection techniques are readily applied. It is desirable to provide a measuring apparatus that can be utilized on the production floor to do 100% straightness checking. Such apparatus must necessarily be of rugged design, low in cost, and simple to operate. No complex set up or fixturing should be required to utilize the measuring device, and no extensive operator training should be necessary.
The present invention is directed to overcoming one or more of the problems as set forth above.